1. Field of the Invention
The present invention is directed to a method for the automatic alignment of a medical instrument with reference to a target point in the body of a patient, for example for subsequent removal of a tissue sample or for therapy of a tumor in the target point, using a computed tomography apparatus (with fluoroscopy mode).
2. Description of the Prior Art
A method for the alignment and introduction of a medical instrument to a target point in the body of a patient is known wherein the attending physician aligns a medical instrument at the paracentesis point of the body of the patient, perforates the skin and approaches the target point with imaging assistance using a computed tomography apparatus with fluoroscopy mode. The computed tomography apparatus with fluoroscopy mode thereby supplies image sequences of up to eight images/second (frames/second), so that the attending physician can observe the paracentesis motion directly at the picture screen.
In order to avoid direct exposure to X-rays, the attending physician grasps the medical instrument with forceps or tweezers, resulting in an indirect and impractical manipulation of the medical instrument.
An object of the present invention is to provide a method for alignment of a medical instrument with reference to a target point in the body of a patient that is automated and has an improved targeting precision.
The above object is achieved in accordance with the principles of the present invention in a method for automatically aligning a medical instrument relative to a target point in a patient""s body, such as for subsequent removal of a tissue sample or for therapy of a tumor in the target point, using a computed tomography apparatus with fluoroscopy mode, wherein the paracentesis tip of a medical instrument is positioned at a paracentesis point of the patient""s body using an automated guidance system, and wherein the medical instrument is positioned using the guidance system into a first position within a CT image plane that contains the paracentesis point. The spatial coordinates of the medical instrument at the first position are determined and stored. The medical instrument is then positioned by the automated guidance system into a second position within the CT image plane that differs from the first position. The spatial coordinates of the second position are determined and stored. The spatial coordinates of the CT image plane are then determined from the stored spatial coordinate for the first and second positions of the medical instrument.
Thus, the medical instrument in the inventive method is aligned with reference to a first CT image plane. As a result, the spatial coordinates of the first CT image plane are communicated to the guidance system of the medical instrument. The guidance system (xe2x80x9cguide robotxe2x80x9d) that, for example, is motor-driven or pneumatically driven, can be attached to or in the proximity of the computed tomography apparatus without prior registration of its own spatial coordinates.
If, in the subsequent introduction of the instrument into the body of the patient, the paracentesis tip deviates from the previously defined, extended axis proceeding from the paracentesis point to the target point due to patient and/or organ movement, this can be automatically registered. The perforation procedure is then interrupted, corrected as needed, and then resumed.
Given a renewed perforation procedure, a correction angle can be taken into consideration in the guidance of the medical instrument, this correction angle, for example, being derived from the deviation of the extended axis, between the paracentesis location and the target point, and the initial, incorrect perforation channel of the medical instrument.
In an embodiment of the method, the paracentesis point at the patient body is located in the first CT image plane, whereas the target point in the patient body is located in a second CT image plane differing from the first plane.
In another embodiment of the method, both the paracentesis point at the patient body, as well as the target point in the patient body, are located in the first CT image plane